This invention relates to a loudspeaker and more particularly to improvements in a dome speaker in the field of electric sound apparatus.
As shown in FIGS. 28 and 29 of the accompanying drawings, the dome speaker of the prior art generally comprises a magnet 11', center pole 12', a front plate 13', a back plate 14', a diaphragm 15', a voice coil 16' mounted on a bobbin 16a' secured to the outer periphery of the diaphragm 15' and disposed in a magnetic space between the center pole 12' and the front plate 13', and an edge 5' supporting the diaphragm 15'. The voice coil 16' is energized with audio currents to activate the diaphragm 15' whereby sound waves are radiated.
The diaphragm 15' is in most cases formed of a light and highly rigid material such as duralumin in order to maximize partial vibration frequency to produce excellent frequency characteristics. Other known dome speakers, so-called soft dome speakers, use a soft material for the diaphragm involving a great internal loss.
Of the examples noted above, the diaphragm formed of a highly rigid material involves a small mechanical internal loss in the diaphragm material. Therefore, in a frequency range higher than the piston vibration range, the vibrating energy conducted from peripheries of the diaphragm and the vibrating energy reverberated from the center of the diaphragm interfere with each other thereby to create a nodal line to anti-resonance adjacent the outer peripheries of the diaphragm. Since the vibrations of the diaphragm are in opposite phases across the nodal line, a dip is formed in the anti-resonance frequency in the frequency characteristics, and a peak is formed in a subsequent high resonance frequency range. This deteriorates the frequency characteristics and transient characteristics to the detriment of aural quality.
In the case of the known soft dome speaker, although the diaphragm is relatively free from resonance and anti-resonance because of the great internal loss, the large mass of the diaphragm and the difficulty in conducting vibrating energy render the speaker very inefficient in energy conversion.